The proliferation of hard disk drives in recent years has been remarkable, and these drives are now installed in a wide variety of data devices, from personal computers and video recorders to portable music players. More recently, one-inch hard disk drives with capacities of 5 GB have appeared on the market, and reductions in the size and profile of these hard disk drives are progressing rapidly. It is expected that hard disk drives will be extensively installed in mobile telephones in the future.
FIG. 18 is a schematic exploded perspective view showing the structure of a conventional hard disk drive.
As shown in FIG. 18, this hard disk drive 70 has a platter 11 which is the recording medium; a spindle motor 12 for rotatably driving the platter 11; an arm 14 with a magnetic head 13 attached to a distal end thereof; a bearing 15 that supports the rear end of the arm 14; a voice coil motor 16 for slidably driving the arm 14; first and second circuit substrates 17, 71 that are components of respective functional block control circuits; a metal casing 18 that houses and electrically shields these components; a metal casing cover 19; and a shielding plate 72 for covering the exposed surface of the second circuit substrate 71. The first circuit substrate 17 has a connector 20, and a lead opening 18a for bringing out the connector 20 from the casing is formed on the bottom surface of this casing 18. The first circuit substrate 17 and the second circuit substrate 71 are therefore connected by the connector 20. A head amplifier IC 41 is mounted on the first circuit substrate 17, and a flexible printed substrate 21 is used for connecting the head amplifier IC 41 and the signal line on the side of the arm 14 in order to allow natural functioning of the arm 14.
FIG. 19 is a schematic side cross-sectional view showing the hard disk drive 70 of FIG. 18 in an assembled condition.
As shown in FIG. 19, the platter 11, spindle motor 12, arm 14, voice coil motor 16, and the first circuit substrate 17 are all accommodated by the casing 18, and the opening of the casing 18 is shielded by the metal casing cover 19. Grooves (indentations) 18b, 18c are provided to the bottom surface of the casing 18 in order to house the bearing 15 for the arm and the spindle motor 12. The spindle motor 12 and arm bearing 15 are respectively housed and fixed in corresponding indentations 18b, 18c. 
The first circuit substrate 17 is provided inside the casing 18 in regions other than those of the platter 11 or the like. The first circuit substrate 17 therefore has a long, thin irregular shape, and is not a simple rectangular substrate. As a result, the first circuit substrate 17 is provided in a small space inside the casing 18. The substrate surface area is therefore comparatively small, and the number of components that can be mounted is also limited. Consequently, a second circuit substrate 71 is required as another circuit substrate for mounting other circuits that cannot be mounted on the first circuit substrate.
The second circuit substrate 71 is provided outside the bottom surface of the casing 18, and the exposed surface thereof is shielded with a shielding plate 72. The depressions 18b, 18c which are the mounting sites for the spindle motor 12 and voice coil motor bearing 15 appear as protrusions when viewed from the back side of the casing 18, and the second circuit substrate 71 is provided to a region other than these protrusions. In other words, the second circuit substrate 71 is not a simple rectangular plate, but has a shape produced by punching out circles in the regions corresponding to the protrusions. The second circuit substrate 71 is connected to the first circuit substrate 17 via a connector 20.
The head amplifier IC 41 and peripheral components are primarily mounted on the first circuit substrate 17. The head amplifier IC 41 is an analog circuit, and has a read amplifier for data recording and a write driver for reading. These components are used for amplifying signals that have been read by the magnetic head and for amplifying the current used for the write signals. In order to minimize noise effects, the head amplifier IC 41 is preferably provided as close as possible from the head assembly, and is mounted on the first circuit substrate 17 for this reason.
A read/write channel IC, motor driver IC, hard disk controller IC, microcomputer IC, memory IC, and peripheral parts thereof are mounted on the second circuit substrate 71, and these ICs are connected by bus lines. The read/write channel IC decodes and modulates the write data and outputs the data to the head amplifier. Conversely, the data from the waveform that has been read, or the output signal from the head amplifier, is detected, encoded, and demodulated. The motor driver IC controls the spindle motor and the voice coil motor. The hard disk controller IC, as the name implies, is a circuit that controls the hard disk, and the components thereof include an error correction circuit, a buffer control circuit, a cache control circuit, an interface control circuit, and a servo circuit. The microcomputer IC controls the hard disk drive as a whole, and primarily carries out control of head position, interface control, peripheral LSI settings and initializations, and defect management.
FIG. 20 is a schematic external perspective view showing the structure of a mobile telephone that has the aforementioned hard disk drive 70, and depicts a condition in which the keypad has been removed.
As shown in FIG. 20, this mobile telephone 80 has a fold-up configuration, and the upper casing 51 and the lower casing 52 of the mobile telephone 80 are rotatably connected via a hinge 53. A main display 54 and camera 55 are provided to the upper casing 51. A main substrate 81 and antenna 59 are also accommodated in the lower casing 52. Although not shown in the drawing, a battery pack, speaker, and the like are housed in the bottom of the main substrate 81, and the hard disk drive 70 is also disposed therein. During actual use, the keypad 63 is attached to the top surface of the lower casing 52.
FIG. 21 is a schematic side cross-sectional view showing the internal structure of the mobile telephone 80.
As shown in FIG. 21, the interior of the upper casing 51 has a main display 54, camera 55, bottom surface display 56, and drive circuits (57) for these components. The interior of the lower casing 52, on the other hand, has a main substrate 81, an antenna 59, a battery pack 60, a speaker 61, a hard disk drive 70, and a keypad 63.
An RF component 58a, a power source 58b, an image processor 58c, and a baseband component 58d of the mobile telephone 80 are all components disposed on the main substrate 81 in the lower casing 52. The hard disk drive 70 is provided under this main substrate 81. The hard disk drive 70 and main substrate 81 of the mobile telephone 80 are connected via a flexible printed substrate 62.
The prior art related to wireless data terminals having hard disk drives has been described in various other documents such as Japanese Laid-open Patent Application 2004-362523 and 2001-285179.
As described above, the demand for smaller and thinner hard disk drives has been increasing, but platter sizes as well as the sizes of various motors and manufacturer parts are still difficult to make smaller, and thus novel designs involving different methods are required in order to achieve additional reductions in size and thickness of hard disk drives.
In addition, with conventional hard disk drives, numerous digital ICs have been mounted on the second circuit substrate 71, but when hard disk drives that are exposed to the external environment are mounted in mobile telephones unmodified and without shielding the second circuit substrate 71, the wireless circuits of the mobile telephone will be affected by high-frequency noise or unwanted radiation generated by the digital ICs or the bus lines that connect the circuits. As a result, there is the danger that the transmission quality of the mobile telephone will be impaired. In particular, this interference will have a significant influence on reception sensitivity of mobile telephones that use frequency spread coding such as CDMA.
As shown in FIGS. 18 and 19, it is possible to individually shield the wireless circuits on the mobile telephone by a means such as shielding the second circuit substrate 71 using a metal plate 72, but because parts that are susceptible to the influence of noise are each shielded in extremely small and thin mobile telephones, it is difficult to additionally reduce the thickness of the mobile telephones.
Moreover, although multiple digital ICs constitute the baseband component 58d of the mobile telephone 80, the noise that is generated by the baseband component 58d exerts a detrimental influence on the RF component 58a and the power source 58b in the mobile telephone. Frequency spread formats such as CDMA (code division multiple access) are particularly susceptible to in-band noise, and thus effects on mobile telephones that employ frequency spread coding are extreme.